1. Field of the Invention
The present invention relates to a method for producing a high-zinc-content yeast extract which contains zinc derived from a natural product in a high concentration, which is excellent in water-solubility, which can ameliorate zinc deficiency-associated dermatitis and dysgeusia; and which can be suitably used as an oral or tube feeding composition (e.g., a liquid food) or a food material; the high-zinc-content yeast extract; food (e.g., a liquid food and a beverage) containing the high-zinc-content yeast extract; and an agent for maintaining and restoring a green color of vegetables.
2. Description of the Related Art
According to the data recently published by Ministry of Health, Labour and Welfare, the daily zinc requirement is about 10 mg in adult males, and about 8 mg in adult females. Zinc deficiency in vivo has been well known to cause dermatitis and dysgeusia, and potentially causes chronic diarrhea, hypoalbuminemia, pancytopenia, growth disorder, and gonadal dysgenesis (see “Dietary Reference Intakes for Japanese 2010,” Ministry of Health, Labour and Welfare, the report from the Scientific Committee of “Dietary Reference Intakes for Japanese”, published by DAI-ICHI SHUPPAN Co. Ltd., p. 227-230 (2009 Sep. 20)). Therefore, there is a need to develop a safe food material for a liquid food or a beverage which allows for efficient ingestion and absorption of zinc into a living body, and which can ameliorate zinc deficiency-associated dermatitis and dysgeusia. Yeast has been utilized as a food material by human since a long time ago. For example, brewer's yeast has been utilized as a source of supply of dietary fiber, vitamin, or mineral. Especially, yeast into which zinc has been uptaken or extract thereof is thought to be available as a safe zinc-enriched food material.
However, in conventional zinc-containing yeast, a distinctive odor such as a yeast odor and a distinctive taste such as a yeast taste are insufficiently reduced, making it unsuitable as a food material. The conventional zinc-containing yeast is water-insoluble, so that turbidity and precipitation are caused when it is added to food. As a result, the conventional zinc-containing yeast cannot be used in, especially, a soft drink, which is problematic.
In order to solve the above problems, there has been proposed a zinc-containing yeast extract which is extracted from the zinc-containing yeast. Extraction of a yeast extract from mineral-containing yeast (e.g., zinc-containing yeast) has been performed by, for example, the following methods: (1) a hot-water extraction method, (2) an autolysis method, (3) an enzymolysis method, and (4) a hydrolysis method with hydrochloric acid or sulfuric acid (see Hiroshi Sugimoto, “Transition of yeast extract production method (I)—from the trend of patent applications in Japan—,” New Food Industry 1994, Vol. 36, No. 10, p. 41-48). However, the methods of (1) to (3) have a problem of a low mineral recovery rate (zinc extraction rate). The methods of (2) and (3) have a problem that a yeast odor and an extract taste remain in the resultant yeast extract. The method of (3) has problems of a high cost and a residual enzyme in the resultant yeast extract. The method of (4) has a problem that a counter ion of the mineral (e.g., chlorine ion or sulfate ion) may remain in the resultant yeast extract, making the yeast extract unsuitable for a food material.
Metals such as zinc have a possibility to be used for restoring a green color of vegetables. It has been known that the green color of vegetables (including processed vegetables) is disappeared due to a change of chlorophyll during processing (e.g., blanching, heat sterilization, drying, fermentation, and salting) and during storage. Therefore, in, especially, food processing industry, there has been a demand to maintain the green color of vegetables for a long period of time, because maintenance of the green color of vegetables affects shelf life of food and processed products thereof. However, a safe metal-containing material capable of being added to food has not been known, and maintenance of the green color of vegetables for a long period of time has not been achieved.
Therefore, there has been demanded a method for efficiently producing a high-zinc-content yeast extract which has sufficiently reduced distinctive odor (e.g., yeast odor) and distinctive taste (e.g., yeast taste), and which is suitable as a safe food material; the high-zinc-content yeast extract; food (e.g., a liquid food and a beverage) containing the high-zinc-content yeast extract; and an agent for maintaining and restoring a green color of vegetables.